FOOD. Science. Technology. Quality

Food. SCIENCE. Technology. Quality

Food. Science. TECHNOLOGY. Quality

Food. Science. Technology. QUALITY




Structure and functionality of barley starches


Amylose contents of prime starches from non-waxy (regular) and high-amylose barley determined by colorimetric method were 24.6% and 48.7% respectively, while the waxy starch showed only a trace (0.04%) of amylose. The isoamylase debranched amylopectin showed little difference between non-waxy and high-amylose barleys, while amylopectin from waxy barley had significantly higher percentage of fraction with degree of polymerization (DP) < 15 (45%). The x-ray diffraction pattern of waxy starch differed from non-waxy and high-amylose. Waxy starch had sharper peaks at 0.58 nm, 0.51 nm, 0.49 nm and 0.38 nm than non-waxy and high-amylose starches. The d-spacing at 0.44 nm characterizing the amylose-lipids complex was the most evident for highamylose starch but was not observed in waxy starch. DSC thermograms of prime starch of non-waxy and high-amylose barleys exhibited two prominent transition peaks: one above 60°C corresponded to starch gelatinization, and the second above 100°C corresponded to the amylose-lipid complex. The starch from waxy barley had only one endothermic peak of gelatinization of amylopectin with an enthalpy value of 16.0 J/g. The retrogradation of gelatinized starch of three types of barley stored at 4°C showed that amylopectin recrystallization rates of non-waxy and high-amylose barley were comparable when recrystallization enthalpy was calculated based on the percentage of amylopectin. No recrystallization peak of amylopectin was observed in waxy barley. Storage time showed a strong influence on the recrystallization of amylopectin. The enthalpy value for non-waxy barley increased from 1.93 J/g after 24 hr of storage to 3.74 J/g after 120 hr. When gel was rescanned every 24 hr a significant decrease in enthalpy was recorded. A highly statistically significant correlation (r = 0.991) between DSC values of retrograded starch of non-waxy barley and gel hardness was obtained. The correlation between starch enthalpy value and gel hardness of starch concentrate indicates that texture of gel was mainly due to its starch structure and functionality. The relationship between properties of starch and starch concentrate might favor the application of barley starch concentrate without the necessity of using the wet fractionation process.